National Television System Committee (NTSC) and Phase Alternating Line (PAL) are two main television systems used in the world, NTSC is commonly used in the areas of North America, Canada, Mexico, Japan, Taiwan etc.; PAL is commonly used in the areas of Europe, Hong Kong and middle east.
In the NTSC system, while using the interlace scan method to constitute a displaying image, the displaying image is composed of two separate picture frames. Referring now to FIG. 1, which is a schematic representation showing an interlace scan. When scanning an image 100 with 525 scan lines using interlace scanning, those odd scan lines, such as 1, 3, 5, 7, 9, . . . , are first scanned to form a picture frame, and then those even scan lines, such as 2, 3, 4, 8, . . . , are scanned to form another picture frame, and then these two picture frames are combined into a displaying image representing the image 100. Due to the displaying image generated by the interlace scan method requires the combination of the frames of interlace scanning, the displaying image usually suffers the intermittent scintillation effect, concurrent phenomenon and vertical edge zigzag phenomenon, etc.
As for the PAL system, the composition of displaying image is similar to that of the NTSC system and the detailed description is omitted here. For enabling a displaying image to have a better displaying quality, the so-called digital TV system is under development, which adopts the progressive scan method to constitute a displaying image. Please refer to FIG. 2, which is a schematic representation showing a progressive scan method. When scanning an image 200 using progressive scanning of sequentially scanning the scan lines of the image 200, i.e. it follows the order of 1, 2, 3, . . . , 8, . . . to scan the scan lines to constitute a displaying image of the image 200, wherein the progressive scan frequency has been increased from 15.75 KHz to the 31.5 KHz. By virtue of this, the displaying image generated by the progressive scan method shows a relatively less scintillation, and has better image stability and more gentle appearance, so that human eyes will not fatigue as easy while watching digital TV, even for a long time.
Thus, digital TV system is going to be the main stream of future TV system. If a user has the TV adopted the interlace scanning and the TV adopted the progressive scanning simultaneously, or any one of them during a transition period of transforming from NTSC system into digital TV system, a method and device capable of displaying progressive and interlace TV signal simultaneously will be in great demand.